A trackball should be understood to be an assembly comprising a fixed body and a moving part such as, for example, a sphere. The fixed part comprises sensors making it possible to deliver information representative of the position of the moving part relative to the fixed part. The information is associated with a position on the screen by means of a computer of the equipment. An operator displaces the moving part with the fingers to reach a desired position on the screen and thus point to an object displayed on the screen.
The invention is of particular use for a trackball belonging to equipment mounted on board an aircraft. The trackball can then be used to select flight parameters displayed on the screen of the system. More generally, the trackball makes it possible to point to objects displayed on the screen.
The aircraft may be subject to turbulences which risk disturbing the pointing of the objects. More specifically, the turbulences generate vibrations that can result in uncontrolled movements of the moving part of the trackball. Even in the absence of established turbulences, slight acceleration phenomena undergone by the equipment prevent the crewmembers from pointing to a graphic area beyond a certain precision.
A common solution to this problem consists in overdimensioning on the screen the objects that can be designated so as to take into account this limitation. Consequently, this reduces the number of objects that can be displayed on a given display surface.
Attempts have also been made to stabilize the hand of the operator by creating suitable bearing surfaces. One example is given in the patent application published under the number EP 1 552 376 where the fixed part of the trackball has an ergonomic shape intended to receive the palm of the operator, hence its name “palm rest”. Nevertheless, such a palm rest does not make it possible to completely steady the fingers of the operator.
Attempts have also been made to generate an attraction of the pointer in its displacement on the screen. In other words, when the pointer enters into the immediate vicinity of an object to be selected, this attraction provokes a decoupling between the movement of the pointer and the movement of the hand, which has the effect of breaking the illusion of direct designation and fairly systematically leads to the rejection of such solutions on the part of the users.